In recent medial treatments, there are increasing cases where electronic devices (sensors) are mounted on a human body for treatment, and diagnosis of the human body. In this respect, attention is paid to studies on body area network (BAN) systems that establish wireless communication links between sensors mounted on a human body and a coordinator to implement wireless communication. Construction of a BAN system, among those BAN systems, which is focused on faster communication, ease in usage and reliability in order to acquire examination data on a patient in real time, is being progressed.
A conventional body area network (BAN) uses a network second layer (Media Access Control (MAC)) specified in IEEE 802.15.4, the short-distance wireless communication specifications for a personal area network (PAN). In obtaining a synchronization timing in time division multiple access (TDMA), this MAC employs a system of synchronizing with a coordinator based on the counter number of an accurate sequence number (counter) each sensor has. Devices with such a counter function have large power consumption, and are assumed on sensors that operate on a size AA battery of 2000 mAH or so. However, some of the sensors operating on a button battery of 2000 mAH or so do not have the hardware structure that generate such a sequence number, and are undesirably unable to achieve communication using MAC compliant with IEEE 802.15.4.
According to the TDMA synchronization specified in IEEE 802.15.4, a sensor receives a beacon (synchronization message) from a coordinator to take a timing. According to this system, however, the sensor always stands by for an incoming beacon, which undesirably increases power consumption.
There have been proposed several short-distance wireless communication systems assumed on their adaptation to a BAN (see, for example, Patent documents 1 and 2, and Non-Patent document 1). A short-distance wireless communication system generally executes wireless communication achieved on the assumption of the distance of 100 m or less (Bluetooth, IrDA, IrSimple, IrSS, NEC, Piconet, UWB, Wibree, Wireless USE, and Zigbee), and does not need to generate a sequence number in the sensor. In addition, there have not been proposed methods of reducing occasions where sensors stand by for data, thereby reducing the power consumption of the sensors as much as possible, even when the individual sensors constituting a BAN have different timer accuracies.